Preparation of two new polyaldehyde compounds derived from the oxidation of starch and cellulose which bind selectively urea and/or ammonia when introduced into the gastrointestinal tract of patients in chronic uremia. Clinical studies to assess their clinical effectiveness in reducing blood urea nitrogen and the total urea burden in uremic patients and, when used in combination with activated charcoal, the levels of other uremic subtances as well. Determination of the feasibility of using these sorbents as a means to decrease the frequency of expensive and time-consuming hemodialysis (or peritoneal dialysis) in uremic patients who are dependent on dialysis for life maintenance. Also, determination of the feasibility of using these sorbents in conjunction with the Giordano-Giovannetti selected low-protein diet in uremic patients as a means of reducing the total burden of uremic substances, thus permitting a liberalization of this very strict dietary regimen. Also, utilization of these sorbents in regeneration and recycling of dialysate solutions in